A few cases of domestic violence have been in the news lately. Over the last few years there have been many instances of players in the news for being arrested and otherwise being in trouble with the law. These can be for violent acts, drug possession, speeding, and other infractions.
Obviously, football is a violent sport where it isn't only allowed to be violent, it's demanded. And the players have testosterone raging through their system as well which is obvious from their hyper-masculine physiques, so it would seem easy to conclude that they are more violent than the average male, especially since they are rich, privileged, and used to being worshipped for their physical accomplishments.
The thing is, you'd be wrong.
According to this academic study, the frequency of domestic violence among NFL players is considerably lower than among males in the general population.
For a more readable discussion, there is this Huffington Post article.